This invention relates to apparatus which determines whether the duty cycle of a periodic signal produced by an incremental encoder is within a predetermined acceptable range.
Incremental encoders are used to provide sinusoidal timing signals in response to angular displacement usually of a shaft or drum. Often, these signals are converted to square waves, since square waves are compatible with conventional high-speed digital control electronic logic such as TTL, HTL, and MOS. For either a periodic sinusoidal or periodic square wave signal, we will define the term "duty cycle" in relation to a specified period of such signal as that duration of the period when timing information is provided divided by the total duration of the period expressed as a percent. Noise can be caused by mechanical vibrations or by electrical interference. If the periodic signal is subjected to noise, and the timing information is no longer accurate, the duty cycle will be outside of an acceptable range. It is, of course, desirable to detect when a duty cycle is no longer within an acceptable range and to make an adjustment to return it to within such acceptable range so that the timing information is accurate.